Overfeed stoker



May 16, 1939. H. c. CARTER ET Al.

OVERFEED STOKER Filed May e', 1935 2 lsheets-sheet 1V /NNTRE Hama-nen gym/xmas 'A #TURA/5% May 16, 1939.

H. c. CARTER Er AL 2,158,673

OVERFEED STOKER Filed May 6, 1935 2 Sheets-Sheet 2 Patented May 16, 1939 `N UNITED STATES PATENT OFFICE 2 Claims. (Cl. 110,-100

This invention relates generally to overleed stokers and particularly to a stoker employing air for the purpose of conveying coal to the furnace.

5 The main object of vthis' invention is the provision of an exceedingly simple and eflicient means for feeding coal into a furnace above the grates by what is commonly known as overfeeding.v l

The second object is to construct a. stcker wherein the coal supply may be placed at a distance from the furnace, and the number of mechanical parts involved is reduced to a minimum.

The third object is to provide a stoking device u whereby coal of varying proportions of sizes and moisture content may be successfully delivered from a remote source of supply to a furnace by high velocity air, the speed of travel of the fuel being appropriately reduced by changes of di- 20 rection or elevation along the fuel line.

The fourth object is to construct a stoker in which complete and desirable distribution of :nel may be obtained over the entire grate surace.

,26 The fifth object is the construction of a stoker of the class described in which working parts are not subjected to the direct heat of the furnace.

The sixth object is to construct a stoker having y one or more nozzles, making it adaptable to 30 various widths and lengths of gratos and different types of furnaces. and in each instance giving a desired spread of fuel on the grates.

'I'he seventh object is the provision of a stoker of the class described wherein the nes are 35 burned in suspension and the lumps and intermediate sizes are projected uniformly over the grate area..

The eighth object is to construct a stoker which employs a mechanism for controllably feeding a 4@ positive supply of `coal into a conveying air stream, and delivering coal to the air stream with a worm or other form of feeding mechanism in a manner to insure against packing or clogging of the fuel.

The ninth object is to provideV a special form of nozzle for deflecting the fuel and distributing it over the grate area.

The tenth object is the utilization of a variable velocity of the air stream to cause the coal to $0 be spread forwardly and backwardly along the grates.

The eleventh object is to utilize a specialv form of protection against foreign substances, -such as tramp metal, wood, stones, etc., which will prec vent these substances from clogging the Vfuel delivery pipe, or injuring the feeding apparatus itself.

The twelfth object is the construction of a form of overfeed stoker which will render unnecessary the remodeling of the boiler front, the stoker being easily adaptable to any of the existing types of installation.

The thirteenth object is to provide an improved form of holdover mechanism whereby a re may be maintained on the grates during shut w down periods in spite of. the relatively small v depth of fire bed normally carried.l

The fourteenth object is the construction of an improved form of transfer box whereby coal may be delivered from a hopper or bin by a feed- 15 ing mechanism to an air line.

The fifteenth object is to provide ttingsl which are readily accessible at points most subject to clgghg.

We accomplish these and other objects in the 2@ manner set forth in the following specification as illustrated in the accompanying drawing in which:

Fig. 1 is a partially diagrammatic perspective view showing a representative form of the dez5 vice with a boiler' setting broken away in section.

Fig. 2 is a section taken along the line 2--2 in Fig. 1.

Eg. 3 is a section taken along the line I-I in F18- 2- se Fig. 4 is a section taken along the line 4-4 in Fig. 3.

Fig. 5 is a section taken along the line` 5 5 in Fig. 1, showing a representative form of grate employed for this device. 35

Pig. 6 is a side elevation with part broken away showing a modified form of the device including a means for causing a surging in the conveying air supply.

Fig. 7 is a section taken along the line 1-1 in o Fig. 6.

Fig. 8 is a section taken along the line 8-8 in Fig. 1.

Fig. 9 is a section taken along the line 8-9 in Fig. 8. l

Fig. 10 is a perspective view of one form of nozzle employed in this device.

Similar numbers of reference refer to similar parts thoughout the several views.

also drives a fan contained within the casing 25 to which is connected an air discharge duct 26."

At the outlet end of the housing 2| is placed a flanged clean-out section 21 having a removable cover 23. Connected to the section 21 is a anged transfer box 29 having an opening 30 in the top thereof, which communicates with the duct 26 through the downturned end 3| of the duct 26.

'I'he worm 22 has a shaft extending through the transfer box 29, and it has formed along that portion of its length which occupies the transfer box 29, a radial vane 33.

The purpose of this construction is to permit the worm 22 to move coal from the housing 2| into the transfer box 29, and the vane 33 in swinging about the axis of the worm shaft 32, carries coal around with it to the top side of the shaft 32, this coal being blown out by air from the duct end 3| into the coal delivery tube 34, which may go directly into the branch fitting 35, or the tube 34 may contain numerous bends 36 if necessary for the convenient installation of thel stoker.

The lower side 31 of the transfer box 29 is spaced from the under side of the worm 22 for the purpose of affording greater protection against foreign substances.

In Fig. 5 is illustrated a common form of pinhole grate 33, whose openings 39 may be tapering, or they may assume any of the desired form's without departing from the spirit of this invention.

' In Fig. 8 is shown 'an enlarged view of the branch fitting 35, which connects the coal tube 34 with the branch pipes 43. The proportion of fuel delivered to each o f the pipe.. 43 isdetermined by means of an adjustable vane 44 which is pivotally mounted on the truxigons 45, on one of which is attached an operat arm 46, which may be secured in any desired position by means of the set screw 41.

It will be understood that the air that is admitted with the fuel for the purpose of conveying same is referred to as primary or conveying air. and that air which is admitted to the under side of the grates 33 through the duct 56 is referred to as secondary air.

In Fig. l0 is shown a nozzle 55 having a somewhat rectangular outlet 6i, which has disposed at an intermediate point. a divider or spreader 62 for the fuel stream. This may be fixed or adjustable as appears desirable for a given condition.

Adjustable deflector bars 53 are also provided on the nat sides of the nozzles 55, and the ends 64 of the deectors 63 is turned in front of the outlet 5 I Obviously, any number of deectors 63 may be' employed, and their individual or joint width may be varied without departing from the spirit of this invention. y

In the form of the device shown in Fig. 6, the air discharge duct 16 is provided with a revolvable damper 11, which can only partially close the duct 16. r,

0n the shaft 15 of the damper 11 is secured a pulley 19 which is connected by means of a belt 50 to a pulley 0| on the shaft 82 of a toothed agitator wheel 33, which meshes' with the fuel feed worm 22,l the purpose of which is to utilize the movement of the slowly rotating worm 22 and the consequent rotation of the toothed agitator wheel 33 to revolve the damper 11, and produce a surging action of the air owing through the pipe 64; and thereby vary the distribution of fuel ejected from the nozzle 55. 4

Referring again to Fig. l, it willbe seen that the motor 23, which operates the coal delivery, is connected by means of a circuit 91 to a time interval contactor 99, the details of which are not illustrated or described herein as devices of this class are in common use on the market, the same merely operating to close the circuit 91 at fixed intervals of time. The motor 99, which operates the fan |00 for supplying secondary air to the under side of the grates 35, is connected by means of the circuit I0| including the thermostat |02 or equivalent device across the circuit 91 to shunt out the time interval contacter 90. The power is supplied to the circuit 91 from the power line |03.

In the form shown in Fig. 1, fuel from the bin 20 is delivered by the worm 22 to the transfer box 29 from whence it is blown by air from the duct 26 through the coal delivery tube 34 out of the nozzles 55.

It will be observed that the coal is horizontally fed into the transfer box 29, but-that the air is admitted over the top thereof so that the uppermost portion of the coal is blown therefrom, and that moreover, the vane 33 serves to separate portions of the incoming coal and elevate it in a trough between the vane 33 and the shaft 32 thereby facilitating its discharge into the tube 34.

It will be noted that owing to the manner in which the fuel is conveyed by air, it is not necessary that the pipes 34 be in a perfectly straight line. In fact, it is desirable in many instances to provide curves in the pipe for the purpose of reducing the velocity of the co'al passing therethrough.

By controlling the setting of the arm 46, lateral distribution can be regulated at will, and by adjusting the positions of the deectors 53, uniform coverage may be obtained over the entire grate area. This distribution in many cases will be still further improved through the operation of the damper 11 shown in Fig. 6,thereby giving a continuous change in the delivery of the fuel, that is, in a forward and backward direction.

- Since certain types of coal are best burned by the overfeed method and with a relatively thin fuel bed, it is imperative that the distribution be as uniform as possible, not only as far as the depth of fuel is concerned, but also with regard to the proportions of various sizes distributed over the grates; that is to say, it would be objectionable to l As previously stated, because of the wide range of sizes ndable in a given quantity of coal and the great number of diil'erent sizes of coal in use, as well as the variations in the moisture content thereof, it is clear that any one single arrangement or setting cannot possibly suit all wrobable conditions. In addition thereto is the ever present problem of a specific type of equipment, that is to say, other things being equal, the details of our device will be dependent largely upon the particular type of furnace with which it is employed.

The type of nozzle employed is equally dependent upon the requirements of the individual installation. This element will be treated only in a general way in this application. v

One of the problems ,encountered in ovei'feed iiring and occasioned by the relatively shallow fuel bed is the inability to hold a flre over any coni siderable shutdown period unless suitable preparations are made. This is commonly done by means of a scoop shovel, the fireman merely piling coal on a portion of the gratesto hold the fire; but our.device, by use of a time interval contactor 98 supplies coal. and primary or conveying air alone to the combustion chamber at timed intervals while there are no calls for heat; but

when there is a call for heat, for example, as in` dicated by the thermostat |02, then the stoker not only feeds coal and primary air, due to the operationof the motor 23, but also secondary air, due to the operation of the motor 99. 'Ihat is, when heat is not required, only enough coal and air are furnished to maintain the' fire in readiness for any call for heat from the thermostat |02 or equivalent device.

It will also be noted that owing to the means which we employ to convey fuel into the furnace, no special furnace front is required, and only a very limited amount of alteration is needed to install this equipment in any furnace.

We claim:

1. In a stoker, fuel feeding means, a motor for driving said means. a blower. a second motor for driving said blower, a thermal switch, a power circuit including in series, said switch and both motors, and time controlled means shunting the blower motor and the switch to complete at timed intervals a shorter power circuit including the fuel feeding motor, whereby whenever the thermal switch is closed both motors operate but when the thermal switch is open, rthe time controlled means closes the shorter circuit and the fuel feeding motor operates alone.

2. In an overfeed stoker having a grate. means for discharging fuel and air above the grate, a motor for driving said means, a blower for discharging air beneath the grate, a motor for driving the blower, a circuit including -a heat responsive switch for energizing both motors, Aand time controlled means shunting the thermal switch and the blower motor for causing the fuel feed motor to operate at regular intervals of .time for chosen periods to keep the fire alive in absence of calls for heat, whereby combustion air will be delivered below the grate in response to a call for heat but will not be delivered upon a timed feeding to keep the fire alive.

HASKELLC. CARTER. THOMAS A. MARSH. 

